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couple questions from a newb carb tuner

Old 09-19-2006, 09:53 AM
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couple questions from a newb carb tuner

let me set one thing straight. i know very little about carbs. it may come as a surprise. especially if you own a turbo honda or acura, especially if you own a turbo accord or prelude and use a little fuel management program called uberdata. i helped design the fuel and timing maps for those cars. so onto the topic of this discussion. i have very little experience with carbs and am looking for a little feedback.
98 shawk
17k mi almost
...and its rich...:-)
black plugs, popping, 22-24 mpg, the whole nine yards.
current mods:
stock airbox new filter, new plugs, cut header at x pipe, installed 2 2" 45* bends and a single 15" two bros. muffler out the right side. just removed the emissions garbage. the plates leak a little....i was in a rush this morning.

so onto my questions:
These babies are extremely sensitive with exhaust leaks from the pair removal, eh? major power losses like 20hp....guess i got used to turbos too much.
how the hell do i richen and lean the a/f mixture? i have had most of this baby apart, so technical answers are ok. just curious on the procedure and location of adjustment points.

i appreciate ya'lls help and i promise i will get pics up asap, but im too busy RIDING in the beautiful texas weather. even if i do get 22 mpg...
in addition, hello all.
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Old 09-19-2006, 11:16 AM
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I think it sounds like you out of the range of adjustment and perhaps need to re-jet the carbs. More guys with more experience will be on later. Good Luck!
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Old 09-19-2006, 03:51 PM
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Originally Posted by nuhawk
I think it sounds like you out of the range of adjustment and perhaps need to re-jet the carbs. More guys with more experience will be on later. Good Luck!
range of adjustment eh? where would i find this gold mine?
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Old 09-19-2006, 06:41 PM
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Okay, so you're running stock filter, stock airbox, and a 2-into-1 exhaust. I can give you some ideas, but I've not yet dealt with jetting a 2->1 on the VTR yet. The popping you hear is a result of PAIR. Do a search on the forum and I also have some info on my site.

You need to pull the tank, airbox, and carbs. If lots of gas comes out of the petcock when you take the hose off you will need to shut the petcock with an 8mm wrench. Carb removal requires removal of choke cable (gently, it's a plastic fitting), both throttle cables, carb heating hoses, and I think the fuel hoses can stay on. Loosen the clamps on the boots. Rock carbs side to side while pulling them out.

Take the carbs to a nice clean workbench. First take off the diaphragm covers (black). Screws can be tight. Slowly remove covers as to not tear the diaphragms. They are fragile. There's also a long-*** spring that'll pop out at you. Slide the diaphragm and carb slide out. Now take one of the cover screws and screw it into the middle part of the carb slide. This is a retainer that holds the needle in. Pull it with a pair of pliers and it'll come right out. Inspect the o-ring. Now remove and inspect the needle. If it has slots in it this is a good thing. That means it has an aftermarket jet kit, and is also adjustable via the little clips. If it has none then you're going to want to buy one. Stock needles can be raised, but not lowered. Lowering the needle will get you leaner. This is what you want. If it's aftermarket, then move the clip to a higher position (closer to the end). Put everything back together. To make assembly easier, compress the spring into the hole in the cap, and then slip the slide assembly over where the spring is. Install the 3 parts together on the carb. Diapragm should be concave down. Careful not to pinch the diagphragm.

Next, the float bowls need to come off. These screws are super tight from the factory. I recommend using a really good screwdriver and a hammer (as a sort of impact driver) as to not strip the screws. Now once the bowls are off, the main jets are the ones that screw in with a flat bladed screwdriver and will have a number like 178, 180, 182, etc. These will need to be replaced with ones of at least one size smaller. They come in sizes that change by 2 or 3, as above. The front and rear have different sizes, BTW.

There is a pilot jet, also flat blade, that will have a number like 45, 48, or 50 on it. This should be removed, inspected, and replaced. There are tiny holes in the emulsion tubes that need to be clean. You will prefer the #45.

After all that is done, on the bottom of the carb you'll see a little "D"-shaped brass screw. If you can figure out how to get that out and then slot the end for a flat blade then it'll be easier to adjust. If you order a jet kit then it should come with a tool. You want to adjust these to about 1.75 turns out from fully seated.

Put everything back together and test ride. The small vacuum line does NOT go to the bottom nipple on the petcock. It goes to one on the back of the petcock. Common mistake there. Also, if the petcock was shut, reopen it.

DISCLAIMER: I did this about 6 times when I jetted my bike, so don't expect this to be the first time you tear the carbs down. I'm giving you a decent baseline based on my extensive knowledge of jetting the VTR. By no means should you expect perfection on the first try...but I'm hoping it'll be close.
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Old 09-20-2006, 06:17 AM
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Originally Posted by Hawkrider
Okay, so you're running stock filter, stock airbox, and a 2-into-1 exhaust. I can give you some ideas, but I've not yet dealt with jetting a 2->1 on the VTR yet. The popping you hear is a result of PAIR. Do a search on the forum and I also have some info on my site.

You need to pull the tank, airbox, and carbs. If lots of gas comes out of the petcock when you take the hose off you will need to shut the petcock with an 8mm wrench. Carb removal requires removal of choke cable (gently, it's a plastic fitting), both throttle cables, carb heating hoses, and I think the fuel hoses can stay on. Loosen the clamps on the boots. Rock carbs side to side while pulling them out.

Take the carbs to a nice clean workbench. First take off the diaphragm covers (black). Screws can be tight. Slowly remove covers as to not tear the diaphragms. They are fragile. There's also a long-*** spring that'll pop out at you. Slide the diaphragm and carb slide out. Now take one of the cover screws and screw it into the middle part of the carb slide. This is a retainer that holds the needle in. Pull it with a pair of pliers and it'll come right out. Inspect the o-ring. Now remove and inspect the needle. If it has slots in it this is a good thing. That means it has an aftermarket jet kit, and is also adjustable via the little clips. If it has none then you're going to want to buy one. Stock needles can be raised, but not lowered. Lowering the needle will get you leaner. This is what you want. If it's aftermarket, then move the clip to a higher position (closer to the end). Put everything back together. To make assembly easier, compress the spring into the hole in the cap, and then slip the slide assembly over where the spring is. Install the 3 parts together on the carb. Diapragm should be concave down. Careful not to pinch the diagphragm.

Next, the float bowls need to come off. These screws are super tight from the factory. I recommend using a really good screwdriver and a hammer (as a sort of impact driver) as to not strip the screws. Now once the bowls are off, the main jets are the ones that screw in with a flat bladed screwdriver and will have a number like 178, 180, 182, etc. These will need to be replaced with ones of at least one size smaller. They come in sizes that change by 2 or 3, as above. The front and rear have different sizes, BTW.

There is a pilot jet, also flat blade, that will have a number like 45, 48, or 50 on it. This should be removed, inspected, and replaced. There are tiny holes in the emulsion tubes that need to be clean. You will prefer the #45.

After all that is done, on the bottom of the carb you'll see a little "D"-shaped brass screw. If you can figure out how to get that out and then slot the end for a flat blade then it'll be easier to adjust. If you order a jet kit then it should come with a tool. You want to adjust these to about 1.75 turns out from fully seated.

Put everything back together and test ride. The small vacuum line does NOT go to the bottom nipple on the petcock. It goes to one on the back of the petcock. Common mistake there. Also, if the petcock was shut, reopen it.

DISCLAIMER: I did this about 6 times when I jetted my bike, so don't expect this to be the first time you tear the carbs down. I'm giving you a decent baseline based on my extensive knowledge of jetting the VTR. By no means should you expect perfection on the first try...but I'm hoping it'll be close.
excellent information, thank you. i guess i assumed jet kit richened the mixture so i felt something was seriously wrong. i will tear it apart and see what i come up with. but what you are saying is that if it is indeed the stock setup, than i will not be able to lean out the mixture at all?
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Old 09-20-2006, 07:27 AM
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Yea, what Greg said..... - you might also want to run the bike through the butt-dyno proceedure outlined on the FactoryPro web site before you tear it down. Just to get a starting reference point on what performance changes you end up making as you are trying to dial in a leaner mixture.

http://www.factorypro.com/tech/carbtun.html
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Old 09-20-2006, 07:41 PM
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There are a couple ways to determine if you're rich or lean prior to tear-down. The easiest is to look at the exhaust. Black and sooty is rich. If you pull the choke out a bit while the bike is at normal operating temperature and it starts bogging then you're rich. If it runs better then you're lean.
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Old 09-21-2006, 04:36 PM
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Originally Posted by Hawkrider
There are a couple ways to determine if you're rich or lean prior to tear-down. The easiest is to look at the exhaust. Black and sooty is rich. If you pull the choke out a bit while the bike is at normal operating temperature and it starts bogging then you're rich. If it runs better then you're lean.
more good info. appreciate it. i will post pics soon of my creation. i added a k&n air filter (not oem style), cut the airbox, and many other things. it is currently running great.
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